TUESDAY, Dec. 20 (HealthDay News) -- People suffering from high blood pressure, or hypertension, who keep their blood pressure levels under control may add years to their life, a new study suggests.

In fact, those in the study who took medicine to lower their blood pressure for more than four years reduced their risk of dying from cardiovascular disease over a 20-year period, the researchers found.

"For the first time, we prove that treating high blood pressure prolongs life," said lead researcher Dr. John Kostis, a professor of medicine & pharmacology at UMDNJ-Robert Wood Johnson Medical School in New Brunswick, N.J.

"If you take your medications for a month, you live an extra day," he said. "One day benefit from a month of treatment sounds small, but if you start treatment at 40, for example, then you live a couple of extra years."

Although the antihypertensive diuretic chlorthalidone was used in the study, it really doesn't make a difference which antihypertensive one uses; the benefit in terms of life expectancy should be the same, Kostis said.

"The main thing is to take medication to get blood pressure under control," he said. "Treat your hypertension early so you can benefit from a longer, happier life."

The report was published in the Dec. 21 issue of the Journal of the American Medical Association.

To determine the effect antihypertensive drugs might have on extending life, Kostis and his colleagues used data from the Systolic Hypertension in the Elderly Program (SHEP) trial.

In that trial, conducted between 1985 and 1990, more than 4,000 hypertensive patients were randomly assigned to take chlorthalidone or an inactive placebo. The patients in the study were an average of 72 years of age.

Kostis noted that if chlorthalidone didn't work, patients were given a beta blocker.

At the end of the trial, all of the patients were advised to get their hypertension treated, the researchers noted.

When Kostis' group looked at the 22-year follow-up data in 2006, about 60 percent of the participants had died. Of these, 59.9 percent of those taking chlorthalidone had died as did 60.5 percent of those who received placebo.

The researchers found that life expectancy and survival were longer for those who received chlorthalidone during the trial compared with those given a placebo.

The gain in life expectancy, for death from any cause, linked to treating hypertension was about half a day per month of treatment, they found.

Also, people taking an antihypertensive gained about one day free from cardiovascular death per month of treatment, and had less of a chance of dying from cardiovascular disease than those who had received placebo; 28 percent versus 31 percent, respectively.

Dr. Gregg C. Fonarow, a professor of cardiovascular medicine and science at the University of California, Los Angeles, said that "hypertension is a major modifiable risk factor for heart attacks, strokes, heart failure, renal failure and premature cardiovascular death."

Treatment of adults with elevated blood pressure with antihypertensive medications has been shown in many trials to significantly reduce the risk of fatal and nonfatal cardiovascular events, heart failure and renal failure, he said.

"However, as most trials were three to five years in duration, whether there are long-lasting effects on life expectancy from treating hypertension has not been well-studied," Fonarow said.

This study provides further compelling evidence of the enduring benefits of treating hypertension, Fonarow said.

"With over half of the 76 million men and women in the United States who have hypertension not having their blood pressure well-controlled, improved detection, treatment and control of hypertension is imperative," he added.